1. Field of the Invention
The invention relates to a magnetic bearing element having at least one annular permanent magnet that is surrounded by an annular binding band.
2. Description of Related Art
Magnetic bearing elements of this kind for magnetic bearing arrangements are known. The document DE 38 08 331 C2 discloses a magnetic bearing that comprises two self-contained bearing components: a stabilization bearing and a center-of-gravity bearing. This non-contact bearing system is implemented using annular permanent magnets and at least one further set of magnet rings that have an axial magnetization opposite to that of the first set. Such bearing arrangements are used predominantly in machines that are operated at very high rotation speeds, for example turbomolecular pumps or flywheels.
To prevent the annular permanent magnets of the stabilization bearing from expanding, as a result of the large centrifugal forces occurring at high rotation speeds, to such an extent that the fits existing between the magnets become lost and the magnets burst (or shift in the axial direction and detach from the hub), concentric binding bands made of high-strength non-magnetic material having a high tensile strength, preferably a carbon-fiber material with a high tangential preload, are mounted from outside onto the annular permanent magnets during assembly of the bearing elements. These binding bands exert large, inwardly directed radial forces on the annular permanent magnets, counteracting the centrifugal forces that occur during operation.
A substantial disadvantage is the fact that much of the binding band preload is required simply to close the radial gaps between the concentric magnets, and between the inner magnets and the rotor hub. The extremely large centrifugal forces occurring at very high rotation speed can cause the permissible tensile stresses in the binding band, and the permissible compressive stress in the magnet material, to be exceeded. The consequence is that either the binding bands or the annular permanent magnets are destroyed.